In general, hydraulic motors are used for driving a rotary member such as a wheel, a roller of a roller compactor, a crawler track, etc. Usually, the outlet shaft drives one or more wheels of a vehicle.
It is frequent for it to be necessary to synchronize the speed of rotation of the various rotary members driven by the motors. For example, in a vehicle driven by two wheels disposed on a common axle, it is necessary for said wheels to rotate at the same speed, at least most of the time.
When the driven rotary members are wheels, they are not necessarily wheels that are situated at the opposite ends of the same axle of a vehicle. They may be any wheels that are to be synchronized. In particular, they may be two wheels disposed on the same side of a vehicle. The motors may then be motors used to drive the crawler tracks of a crawler vehicle.
The invention is also applicable to circuits in which the motors do not drive drive members, but rather tools, for example. For simplification reasons, the following explanations are given with reference to wheels being the rotary members driven by the motors, without this constituting a limitation on the scope of the invention.
For synchronizing or coupling a group of hydraulic motors, it is known that a hydraulic transmission device can be implemented that includes a circuit dedicated to synchronization, in which the feed and discharge orifices of a sub-motor of each of the synchronized motors are connected together so as to constitute a loop, i.e. a closed circuit. U.S. Pat. No. 6,662,557 describes such a device.
Unfortunately, that device suffers from the drawback that the hydraulic fluid contained in the synchronization circuit heats up, and that heating can have damaging consequences for the hydraulic transmission device. In addition, due to the head loss in the synchronization circuit, that transmission device has low efficiency.
In addition, that transmission device does not guarantee uniform distribution of power. Only one half of the sub-motors are used to distribute the drive power, the other half being assigned to synchronization. Certain sub-motors are thus used to a much greater extent than others, and the overall life of the transmission device is therefore shortened.
Finally, the hydraulic transmission device that is described is only for synchronizing motors that are made up of two sub-motors each. No solution is proposed for synchronizing motors that are not made up of a plurality of sub-motors.
European Patent EP 0 547 947 describes a hydraulic circuit for driving front and rear wheels of a vehicle. That circuit is proposed for the purpose of providing coupling between the motors connected to the various wheels of a vehicle, in order to prevent the wheels from spinning.
Unfortunately, in that circuit, the drive power is distributed non-uniformly between the various motors or sub-motors. In particular, at least one sub-motor of one of the motors is connected directly to the main orifices of the pump. A priori, it cannot therefore deliver high torque. Conversely, that sub-motor is subjected to relatively high mechanical stress, due to the large pressure difference between its main orifices; and there is a non-negligible risk of the wheel that it drives spinning, on slippery terrain.
The invention applies to a hydraulic circuit including:                at least one primary motor comprising at least first and second distinct sub-motors, the first sub-motor having a feed or discharge first main orifice, and the second sub-motor having a feed or discharge second main orifice; and        at least one secondary motor;        
in which circuit said first main orifice of said at least one primary motor is connected to a first main orifice of said at least one secondary motor via a first series duct.